No one wants to think that the college student down the hall or the serviceman in his barracks is a serial rapist. But when someone commits what's commonly called "date rape" or "acquaintance rape," chances are he'll do it again.

Acquaintance rape — which describes most sexual assaults in the military — isn't typically about missed signals or a one-time error in judgment, as many people think. It's about predators committing multiple crimes, which is why the military's sorry record of prosecuting rapists contributes to what has become a worsening plague.

When the Senate returns next week, it has an opportunity to force real change by approving a much-needed overhaul of the system for prosecuting sexual assaults in the military. The overhaul is championed by Sen. Kirsten Gillibrand, D-N.Y., and publicly supported by 53 senators, including nine Republicans. But the plan faces opposition from the Pentagon and from lawmakers who favor other options that would make some improvements but fall far short of what's needed.

The Pentagon expects to finish this year with the largest number of reported sexual assaults in its history — more than 5,000, or about 14 a day. The increase might indicate more willingness to report rape, a positive step. The vast majority of these assaults are between people who know each other, and a big part of the problem involves repeat offenders.

A 2009 study of recruits at Naval Station Great Lakes in Illinois found that a small group of serial predators committed an average of six rapes or attempted rapes apiece before and during their first year of service.

That was consistent with a 2002 study of nearly 1,900 men at an unidentified university in the Northeast, which found that 76 men had committed nearly 440 rapes or attempted rapes before and during college. They preyed on young, often vulnerable women, using drugs, alcohol and physical force, says David Lisak, a former University of Massachusetts psychologist who conducted the study. They saw the assaults as conquests, not crimes. And because the cases went unreported, they were free to rape again.

Prosecutions alone won't stop rape in the military. Several preventive measures are needed. These include stronger leadership; training for bystanders in how to intervene to get their buddies out of risky situations; and training on how to avoid dangerous circumstances, a controversial step often misinterpreted as "blaming the victim."

The Pentagon and individual services have some promising prevention programs, including one at the Great Lakes naval station. But none will be taken seriously or succeed if perpetrators aren't prosecuted. And the current military system, in which prosecution decisions are made by commanders, simply has not worked.

The decision should be put in the hands of professional military prosecutors, as Gillibrand's measure would require. That's how major criminal cases are prosecuted in the civilian world and by the militaries of many U.S. allies, including Australia, Canada, Great Britain and Israel.

A recent spate of scandals, and increasing numbers of official reports, make change imperative. You can't fight sexual assaults when you leave serial rapists roaming free.

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